A recent study comparing the environmental effects of HFC-134a (R134a) and HFO-1234yf (R1234yf) predicts that the replacement of the former by the latter, such as in mobile air conditioning (MAC), would lead to substantially more production of trifluoroacetic acid (TFA) in the atmosphere, and ultimately on the surface of the Earth.
The study – “Investigation of the Production of Trifluoroacetic Acid from Two Halocarbons, HFC-134a and HFO-1234yf and Its Fates Using a Global Three-Dimensional Chemical Transport Model” – was conducted largely by researchers at the University of Bristol, U.K., and published in March in ACS Earth and Space Chemistry.
Because of its high 100-year GWP (1,430), R134a production is being phased down globally under the Kigali Amendment to the Montreal Protocol. It has been widely replaced in MAC applications by R1234yf, which has a 100-year GWP of less than one.
In the atmosphere, the two gases vary in their degradation into TFA. While emissions of R1234yf completely convert into TFA only 21% of R134a do so, reported a 2017 study by the Norwegian Environment Agency. Moreover, the Norwegian study added, R134a has a lifetime for 14 years while R1234yf breaks down in a matter of days.
The University of Bristol-led study simulated the effects of switching from R134a to R1234yf and found a 33-fold increase in the “global atmospheric burden of TFA.” The amount of TFA would rise from 65 metric tons formed from the 2015 emissions of R134a to about 2,150 metric tons that would be formed in the future from an equivalent emission of R1234yf.
Moreover, in specific geographic areas, the amount of TFA was seen as greater, including an increase of up to 250-fold across Europe and significant increases (up to 50-fold) in regions of the southern hemisphere, under the R134a- replacement-by-R1234yf scenario.
Two outside experts weighed in on these findings in a recent article. “This is – to our knowledge – the first study predicting such high increases in regional TFA depositions. If the findings can be verified, it would most likely mean the end of widespread use of HFOs,” wrote Michael Kauffeld, Professor at the Karlsruhe University of Applied Sciences – Institute of Refrigeration, Air-Conditioning, and Environmental Engineeering, and Mihaela Dudita, Project manager at SPF Institute for Solar Technology, Eastern Switzerland University of Applied Sciences (OST).
The University of Bristol-led researchers also noted that, while their investigation assumed that future R1234yf consumption would match the peak consumption of R134a seen in 2015, “it is likely that [R1234yf] consumption will increase beyond this point and emissions will grow accordingly.” In fact, R1234yf use, they said, is expected to exceed current R134a usage by around 290,000 metric tons per year by 2100.
“This investigation shows that a transition from HFC-134a to HFO-1234yf use will result in a significant overall increase in tropospheric TFA as loss processes cannot compensate sufficiently,” the study says. “As such,
natural cycles of TFA and the proportions that reside in air, land, and sea reservoirs will be altered as environmental contamination increases.”
The University of Bristol-led researchers also studied the ways by which TFA is lost in the atmosphere through a reaction with what are called stabilized Criegee intermediates (SCIs). The effect of SCIs on TFA was found to be greatest over forested regions, such as the Amazon and Congo, where TFA atmospheric lifetime may be reduced to two days from five to 10 days. But SCI-induced loss of TFA is “mostly negligible” over water and ice-covered regions.
Globally, they found that globally these reactions accounted for only about 0.4% of the total loss. “Even with consideration of the effects of SCIs, the percentage increase in tropospheric TFA resulting from the switch to HFO use remains substantial,” their report said.
Another study looking at the accumulation of TFA in rainwater, released last month by the German Environment Agency (UBA), predicted a ten-fold increase in today’s TFA production from R1234yf atmospheric degradation by 2050; this would generate up to 50,000 metric tons of TFA in Europe.
Effects of TFA
In terms of what the additional TFA would do to the environment, the University of Bristol-led study cited a 2020 study suggesting that atmospheric TFA may contribute to the formation of aerosols, “which would have a significant impact on climate change.”
Other recent studies have addressed the potential impact of TFA, a highly durable substance, on the health of humans and other living species.
.While current levels of TFA in the environment are not considered a threat, UBA says in its report that TFA is “classified as hazardous to water.” Moreover, because of the persistence of TFA in the environment and the difficulty of removing it from groundwater and drinking water, the UBA report says that the use of HFOs as substitutes for HFCs “must be regarded as problematic” and encourages the use of natural refrigerants.
Commenting on TFA’s stability in water, Kauffeld and Dudita cited concernsthat “any HFO regulation will come into force too late once the negative consequences of an increased amount of TFA in rainwater becomes evident.” Already, they said, TFA is “not particularly healthy for some aquatic organisms.”
In February, a report released by Refolution Industriekälte GmbH, a Karlsruhe, Germany-based consulting and engineering firm, said that long-term exposure to TFA can potentially damage the liver and the thyroid function in humans.
A spokeswoman for Chemours, a major producer of HFOs, previously defended their use, saying in 2018 that projected future levels of TFA due to continued use of HFOs are still judged to present negligible risks for aquatic organisms and humans. Chemours did not respond to a request for a comment on the University of Bristol-led study.
